BACKGROUND: Recent evidence suggests cardiac progenitor cells (CPC) may improve cardiac function after injury. The underlying mechanisms are indirect, but their mediators remain unidentified. Exosomes and other secreted membrane vesicles, hereafter collectively referred to as extracellular vesicles (EVs), act as paracrine signalling mediators. Here we report that EVs secreted by human CPCs are crucial cardioprotective agents.
METHODS AND RESULTS: CPCs were derived from atrial appendage explants from patients who underwent heart valve surgery. CPC conditioned medium inhibited apoptosis in mouse HL-1 cardiomyocytic cells, while enhancing tube formation in human umbilical vein endothelial cells. These effects were abrogated by depleting conditioned medium of EVs. They were reproduced by EVs secreted by CPCs, but not by those secreted by human dermal fibroblasts. Transmission electron microscopy and nanoparticle tracking analysis showed most EVs to be 30-90 nm in diameter, the size of exosomes, although smaller and larger vesicles were also present. microRNAs most highly enriched in EVs secreted by CPCs compared to fibroblasts included miR-210, miR-132, and miR-146a-3p. miR-210 downregulated its known targets, ephrin A3 and PTP1b, inhibiting apoptosis in cardiomyocytic cells. miR-132 downregulated its target, RasGAP-p120, enhancing tube formation in endothelial cells. Infarcted hearts injected with EVs from CPCs, but not from fibroblasts, exhibited less cardiomyocyte apoptosis, enhanced angiogenesis, and improved LV ejection fraction (0.8±6.8% vs. -21.3±4.5%; p<0.05) compared to those injected with control medium.
CONCLUSION:EVs is the active component of the paracrine secretion by human CPCs. As a cell-free approach, EVs could circumvent many of the limitations of cell transplantation.